Type 1 diabetes mellitus (T1DM) is a heterogeneous autoimmune disease, and both environmental and genetic factors play a role in its pathogenesis. Interleukin (IL)-18 is a potent pro-inflammatory cytokine capable of inducing interferon-gamma production that is associated with the development of T1DM. The gene for IL-18 is located on chromosome 11q22.2-q22.3 and has been reported to be associated with a susceptibility to T1DM. To test the putative involvement between IL-18 gene polymorphism and predisposition to T1DM, we conducted a case-control study in Chinese Han children. The single nucleotide polymorphisms at position -607(C/A) and -137(C/G) in the promoter region of the IL-18 gene were analysed by sequence-specific primers-polymerase chain reaction in 118 patients with T1DM and 150 healthy controls. (1) The allele frequency of -607A was 41.2% and 53.0%, respectively, in patients and in control subjects (P = 0.01), but the allele frequency of -137C/G was not statistically significant (P = 0.37). (2) The distribution of CC genotype at position -607 was significantly different between patients and normal controls (P = 0.03), while the distribution of AA genotype in patients was significantly lower than that in the controls (P = 0.03). (3) Furthermore, there was a significant increase in haplotype (-137C/-607G) and genotype combination (-137GG/ -607CC) in patients compared with controls (P = 0.03 and P = 0.04, respectively). The results of this study show that IL-18 gene promoter polymorphisms confer susceptibility to T1DM in Chinese Han children. Moreover, subjects carrying AA genotype at position -607 of the promoter of IL-18 gene may be a low risk of T1DM development.